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Abstract:

A process that uses targeted in-furnace Injection to feed a fluxing agent
of the chemical family of compositions containing boron and/or alkali
hydrates to either decrease heat transfer on waterwalls of utility
furnaces burning solid fuels to improve steam generation, maintain steam
temperature, and/or allow a protective layer of slag to form inside the
barrels of cyclones on cyclone boilers burning fuels high in calcium so
that the boiler can operate at a wider variety of power settings while
allowing proper flow and drainage of slag from the cyclone barrels.

Claims:

1. A method for controlling slag properties in a cyclone burner of the
type having a barrel fed by a tangential supply of air and coal and a
layer of slag protecting the inside barrel and flowing out of the barrel,
which comprises: providing a boron composition in a liquid vehicle;
utilizing computational fluid dynamics to determine the location, droplet
size, and dosage amount for injection of a boron composition in a liquid
vehicle into a duct for providing air to the cyclone burner, wherein the
conditions of introduction of the boron composition and liquid vehicle
are determined to assure first contact with the duct wall occur no sooner
than after the boron composition has been dried to a fine powder form,
without significantly wetting the wall with the liquid vehicle; injecting
the boron composition in a liquid vehicle into the duct to form a
dispersion of boron composition as a dry powder in air; and directing
flow of the dry powder of boron composition into the cyclone burner in a
tangential flow of air, whereby the fine powder of boron composition
uniformly contacts slag in the cyclone burner.

2. A method according to claim 1, wherein the boron composition comprises
borate, boric acid, borax or blend of two or more of these.

3. A method according to claim 1, wherein the boron composition material
also includes an alkali hydrate.

4. A method according to claim 1, wherein feed of the boron composition
is stopped and feed of alkali hydrates is started.

5. A method according to claim 1, wherein the boron composition is
introduced into a secondary air duct carrying heated combustion air to
the cyclone burner.

6. A method according to claim 1, wherein the boron composition is
introduced into the cyclone barrel with tangentially supplied secondary
air.

7. A method for controlling slag properties in a cyclone burner, which
comprises: utilizing computational fluid dynamics to determine the
location, droplet size, and dosage amount of a boron composition in a
liquid vehicle necessary for slag modification to assure flow of slag
from the cyclone burner while maintaining a protective layer of slag in
the burner; and providing precise dosing as to location and amount of a
boron composition in a suitable vehicle by controlled feeding through
injection ports on each cyclone barrel such that the boron composition
lowers the melt point of the slag while making slag thicker, causing a
protective layer of slag to form on the cyclone barrel inside wall, but
still able to flow to drains.

8. A method for controlling slag properties in a cyclone burner of the
type having a barrel fed by a tangential supply of air and coal and a
layer of slag protecting the inside barrel and flowing out of the barrel,
which comprises: providing a boron composition in a liquid vehicle;
injecting the boron composition in a liquid vehicle into a duct carrying
hot air to the cyclone burner to dray and transport the boron composition
as a dry powder without significantly wetting the wall with the liquid
vehicle; and directing a flow of the dry powder of boron composition into
the cyclone burner in a tangential flow of air, whereby the fine powder
of boron composition uniformly contacts slag in the cyclone burner.

9. A method according to claim 8, wherein the boron composition is
introduced into the cyclone barrel with tangentially supplied secondary
air.

10. A method according to claim 8, wherein the boron composition
comprises borate, boric acid, borax or blend of two or more of these.

11. A method according to claim 8, wherein the boron composition material
also includes an alkali hydrate.

12. A method according to claim 8, wherein feed of the boron composition
is stopped and feed of alkali hydrates is started.

13. A method according to claim 8, wherein the boron composition is
introduced into a secondary air duct carrying heated combustion air to
the cyclone burner.

14. A method according to claim 8, wherein computational fluid dynamics
is utilized to determine the location, droplet size, and dosage amount
for injection of a boron composition in a liquid vehicle into a duct for
providing air to the cyclone burner, wherein the conditions of
introduction of the boron composition and liquid vehicle are determined
to assure first contact with the duct wall occur no sooner than after the
boron composition has been dried to a fine powder form, without
significantly wetting the wall with the liquid vehicle.

15. A system and/or apparatus comprising control means, sensors and feed
devices for effecting the process of claim 1.

[0002] The invention relates generally to improving the operation of
cyclone burners and the combustors or boilers they fire by assuring
adequate slag properties to modulate slag plasticity to a new effective
level, enabling formation and maintenance of a protective layer of slag
on inside wall of a cyclone barrel while assuring a viscosity that
permits the constantly forming slag to flow to drains.

[0003] In particular, the invention provides a system, apparatus and
method for improving the operation of cyclone boilers by increasing
operating flexibility and efficiency of a cyclone furnace while burning
Powder River Basin (PRB) or similar coal by using a specifically
effective fluxing composition in a highly efficient and effective manner.

BACKGROUND OF THE INVENTION

[0004] As originally developed, cyclone burners were characterized as
including a horizontally disposed cylindrical barrel attached through the
side of a boiler furnace. The original design achieved a commercial
following in part because they could take advantage of a variety of coal
grades, including some not suitable for pulverized coal combustion.
Cyclone furnaces will typically spirally feed coal into a combustion
chamber to achieve maximum combustion efficiency. FIG. 1 is a schematic
drawing of a prior art cyclone burner. In addition to providing
flexibility of coal type, they also reduced fuel preparation time and
costs, were smaller and more compact than other furnaces and produced
less fly ash and convective pass slagging.

[0005] These furnaces require a protective layer of slag to be formed and
maintained on the inside of the cyclone barrel wall (12 in FIG. 1) to
provide a degree of insulation for the wall materials. This slag layer is
constantly renewed and drained, and it is essential that the slag
viscosity always permits the slag to flow to drains. The slag must have a
consistency sufficient to maintain the insulating layer, but not be so
thick that it can cool and stop flow to or through drains. The slag
further functions to hold larger coal particles as they continue to burn
as the slag empties from the combustor.

[0006] In these furnaces, the cyclone barrel is typically constructed with
water-cooled, tangential-oriented, tube construction and the burners
include a water-cooled horizontal cylinder in which fuel (coal, gas, or
oil) is fired and heat is released at extremely high rates. When firing
coal, the crushed coal is introduced tangentially into the burner,
usually with primary air. The cyclone barrel extends into the furnace
where it opens to supply burning hot gases and slag to the furnace
interior. Typically during combustion of coal, volatile components are
released from the coal and burn well. However, the fuel carbon results in
"char" particles, which are less volatile and heavier. The char requires
higher temperatures and benefit from the swirling supply of oxygen in a
cyclone furnace, which provides thorough mixing of coal particles and air
with sufficient turbulence to constantly renew fresh air to coal particle
surfaces. The cyclonic fuel swirling in these burners is increased and
maintained by tangentially-introduced, high-velocity secondary air.

[0007] The cyclone barrel is water cooled and cools the slag while the
slag insulates the barrel material as it cools. The cyclone is designed
to operate at high temperatures to maintain the slag in a molten state
and allow removal through the trap. A layer of molten slag coats the
burner and flows through traps at the bottom of the burners. Because the
slag is formed largely within the burners, the amount of slag that would
otherwise form on the boiler tubes in the boiler or other combustor is
reduced. While low volatile bituminous coals, lignite coal, mineral rich
anthracitic coal, wood chips, petroleum coke, and old tires can and have
all been used in cyclones, certain subbituminous coals high in alkaline
earth metals, especially calcium, like Powder River Basin (PRB) coals,
tend to produce slags that suffer from inconsistent properties.

[0008] PRB and like subbituminous coals tend to produce slags that exhibit
a surprisingly sharp drop in viscosity over short temperature spans.
Drops of over 10,000 centipoises can occur in the temperature range of
from 2250° to 2350° F., to a value below the normal
operating temperature of the cyclone boiler. Because it is generally
agreed that stable operation of a slagging cyclone combustor requires the
ash layer to remain molten. The slag viscosity must be low enough to
permit continuous drainage as is illustrated in FIG. 1. A typical
viscosity for steady drainage has been shown to be about 250 centipoises,
and the art refers to the temperature corresponding to this viscosity
level as T250. Stable operation mandates a slag temperature of greater
than or equal to T250. Unless the PRB coal is burned to achieve slag with
the correct viscosity-temperature relationship, the furnace cannot
operate efficiently at any temperature or will be restricted to only
higher loads. The slag can freeze and cause shut down at the low end of a
narrow temperature range or it might run too freely and not provide the
optimum temperature differential at the surface of the water
cooled-cyclone barrel at the high end of the temperature range. If it is
desired to reduce the load, a secondary fuel may be required to just keep
the slag hot enough.

[0009] PRB coals are desired because of their low sulfur contents and
economy, but have proved a challenge to cyclone burner operators, and
efforts have been made to correct the difficulties experienced. Current
remediating technology typically involves feeding iron oxides, e.g., as
made from scale that came from steel plant hot strip rolling plants, into
the furnace on a weight basis with the amount of coal used. This material
will typically arrive dry in rail car quantities and is fed to the fuel
using front end loaders to the fuel hopper. Large quantities of the iron
oxide will be mixed the PRB coal. This method seems to provide poor
mixing, uses excessive quantities of material and is very imprecise.
Furthermore, too much material use also allows the fluxing agent to
escape the cyclone barrels into the greater furnace, causing unwanted and
undesired slagging of heat exchangers.

[0010] As exemplary of iron oxide treatment, Johnson in U.S. Pat. Nos.
6,729,248, 6,773,471 and 7,332,002 describes introduction of iron
containing compounds to act as fluxing agents. The disclosures are
directed to additives for coal-fired furnaces, particularly furnaces
using a layer of slag to capture coal particles for combustion. The
additives include iron, mineralizers, handling aids, flow aids, and/or
abrasive materials. The iron and mineralizers are said to lower the
melting temperature of ash in low-iron, high-alkali coals, leading to
improved furnace performance; but control is difficult. We have assessed
the problems and believe they are caused adding the treatment chemical to
the furnace as a whole, either as part of the fuel or with the combustion
air.

[0011] A different example of using iron agents is found in U.S. Pat. No.
6,613,110, wherein Sanyal employs them to improve heat transfer on the
water-walls of highly-reflective ash-containing boiler furnaces, and does
not mention cyclone furnaces. The disclosed method is said to inhibit
accumulation of light-colored ash on the walls of a furnace in which coal
containing high levels of (coal-bound) calcium is burned. The light color
on the ash surface reflects heat that is then not efficiently utilized
and exits the boiler stack. To correct this, an iron compound is added to
the coal prior to burning the coal, which when burned produces a dark
calcium ferrite that darkens the ash. Other chemicals besides iron
compounds have also been suggested for ash color control in such a
context, and Sanyal cites U.S. Pat. No. 5,819,672 to Radway, which
asserts that boron and metal oxides can act as darkening agents on
furnace water-walls. The disclosed method involves exposing the walls to
a darkening agent, or a combination of a darkening agent and a fluxing
agent. A preferred embodiment involves direct application of the
darkening agent to the water wall. Again, cyclone boilers are not
described, and slag flow from them is not addressed.

[0012] Representative of early efforts for controlling slag in slag tap
furnaces burning higher grade coals, is U.S. Pat. No. 4,057,398 to
Bennett. The patent asserts that boron additives can be introduced into
the furnace box of the boiler as an intimate mixture of pulverized or
crushed coal. Also, U.S. Pat. No. 4,377,118 to Sadowski and U.S. Pat. No.
5,207,164 to Breen suggest the addition of any of a number of fluxing
agents for slag benefit. Sadowski is concerned with decreasing slag
viscosity at the walls of a furnace and employs various slag viscosity
adjuvants formed as particles of significant size and density, noting
that pellets would be sufficiently large whereas a dust would not be.
Bennett is concerned with decreasing the fusion point of coal ash. Breen
utilizes iron, rust or slag for high calcium ash, which is recycled to
the furnace to soften it so that it collects via gravity in a bottom ash
pit. None of these enable increasing operating flexibility and efficiency
of a cyclone furnace while burning Powder River Basin or similar coal by
using a specifically effective fluxing compound in an efficient and
effective manner to increase the flow temperature of the slag with a
minimal use of additive.

[0013] The problem of slag control in cyclone furnaces remains serious but
has not been effectively resolved by the prior art despite years of
effort directed at the problem even with a good understanding of slag
properties, such as might be seen from the text "Influence of Coal
Quality and Boiler Operating Conditions on Slagging of Utility Boilers",
Rod Hatt, Coal Combustion, Inc., Versailles, Ky. This work contains a
wealth of reference material and a discussion on the types of slags
produced by various coals, causes of deposits and procedures for reducing
and removing deposits caused by coal ash. There is, however, no clear
direction on chemical addition control for cyclone furnaces burning PRB
coal that would be absolutely essential for economic and furnace
maintenance reasons.

[0014] There is a present need for a system, apparatus and method for
improving the operation of cyclone boilers by increasing operating
flexibility and efficiency of a cyclone furnace while burning Powder
River Basin or similar coal by using a specifically effective fluxing
compound in an efficient and effective manner.

SUMMARY OF THE INVENTION

[0015] It is an object of the present invention to provide a system,
apparatus and method for improving the operation of cyclone boilers by
increasing operating flexibility and efficiency of a cyclone furnace
while burning Powder River Basin or similar coal by using a specifically
effective fluxing compound in an efficient and effective manner.

[0016] In one aspect, the invention achieves uniform contact of the
burning coal with a precise amount of a boron composition fluxing agent
to improve the flow properties of the slag to assure proper cyclone
furnace operation with coals having low iron and high calcium contents.

[0017] In one aspect, the invention allows dosing of the slag layer formed
on cyclone barrel walls with the precise amount of a boron composition
fluxing agent required to achieve the goal, complete coverage of trouble
spots and no more. The dosing will be guided by problems as observed
and/or calculated and can be prophylactic or remedial. The net effect is
that furnace downtime due to slagging problems will be held to a minimum
while chemical usage will also be greatly reduced from conventional
applications.

[0018] In another aspect, the present invention provides precise dosing as
to location and amount of a boron composition in a suitable vehicle,
e.g., slurry, particulate solid or solution form, by controlled feeding
through injection ports on each cyclone barrel such that the boron
composition, e.g., comprising borate, borax, boric acid or a blend of two
or more of these, lowers the melt point of the slag while making slag
thicker (more plastic), causing a protective layer of slag to form on the
cyclone barrel inside wall, but still able to flow to drains.

[0019] In addition to treating the slag in the cyclone barrel at the
cyclone barrel walls, the boron composition material can be
advantageously applied in a targeted fashion to the water-walls of the
boiler furnace to react with slag thereon to either insulate heat
transfer and allow steam temperature to be maintained in the superheaters
of boilers where superheat temperature is too low due to high furnace
water-wall area, or in a blend with other metal oxides, to improve heat
transfer on the water-walls by decreasing reflectivity of high alkali
earth oxide containing boiler ash.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention will be better understood and its advantages will
become more apparent from the following detailed description, especially
when taken with the accompanying drawings, wherein

[0021] FIG. 1 is a schematic view of a cyclone furnace combustor of the
prior art, showing air and slag flow to help explain material movements
in a burner of this type;

[0022] FIG. 2 is a schematic view of a cyclone furnace combustor, as
viewed from the portion that would extend into the furnace, and showing
one embodiment of flux addition according to the invention;

[0023]FIG. 3 is a schematic perspective view of an exemplary equipment
layout for cyclone burner equipped furnace according to the invention;

[0024]FIG. 4 is a schematic perspective view showing some of the detail
of ductwork for the embodiment shown in FIG. 3; and

[0025]FIG. 5 is a schematic view of an embodiment of the invention with
representative control and material feed arrangements.

DETAILED DESCRIPTION

[0026] Since the invention provides strong advantages in the context of
cyclone furnaces, the following description will refer to such for
clarity and consistency. It will be understood by those skilled in the
art, however, that the principals that make the invention so effective in
that setting will also make it effective in others. FIG. 1, is a
schematic view of a prior art cyclone burner 10, showing air and slag
flow to help explain material movements in a burner of this type. FIG. 2
shows one embodiment of the invention wherein a boron composition is
added directly to the cyclone burner 10 separate from the coal feed.
Reference to FIG. 3 will help understand the arrangement of the of
individual cyclone furnace burners as part of the larger combustor or
boiler, and FIG. 4 will help to better understand the role and importance
of computational fluid dynamics to assure efficient distribution of boron
composition into the cyclone burner.

[0027] The invention will also be described with specific reference to
certain subbituminous coals, like Powder River Basin (PRB) coals, which
tend to produce slags that have a short transition in viscosity as the
temperature varies and otherwise suffer from inconsistent properties. The
burning of these coals in a furnace requiring slag flow, might result in
the slag freezing and causing shut down of the furnace if the operator
wants to operate at less than full load. In other cases, the slag might
run too freely and not provide the optimum temperature differential at
the surface of the water cooled-cyclone barrel. The PRB coals can produce
slags that have a surprisingly sharp drop in viscosity over short
temperature spans. Drops of over 10,000 centipoises can occur in the
temperature range of from 2250° to 2350° F., to a value
below the normal operating temperature of the cyclone boiler.

[0028] It is generally agreed that stable operation of a slagging cyclone
combustor requires the ash layer to be molten, but not too low in
viscosity and not too high. It needs to have a viscosity low enough to
permit continuous drainage as is illustrated in FIG. 1, but not so low
that it runs out of the cyclone burner without retaining the necessary
protective layer of slag. PRB coals often tend to run too quickly at
desirable operating conditions. A critical viscosity for steady drainage
is has been shown to be about 250 centipoises. The temperature
corresponding to this viscosity level is referred to in the art as T250,
and stable operation mandates a slag temperature of greater than or equal
to T250. The invention enables achieving the correct
viscosity-temperature relationship with very low additive levels by
appreciation of the unique operating aspects of cyclone burners and
tailoring a treatment regimen to them, preferably through the use of
computational fluid dynamic modeling.

[0029] While not limited to PRB coals, and generally useful for all
operations with coal-fired cyclone burners, the following provides an
idea of approximate values (dry, weight basis) for coal compositions that
can be successfully burned in a cyclone burner utilizing the present
invention. The coal is preferably fed, crushed as particulates wherein
about 95% passes through a 4 mesh screen. Using crushed coal as opposed
to coal pulverized to a greater degree, mitigates the escape of fines
from the barrel. Other high-calcium and/or low iron fuels can also be
effectively treated according to the invention.

TABLE-US-00001
Total Ash 2-15% of the coal
Si02 20-35% of the ash
Al203 13-20% of the ash
Fe203 3-10% of the ash
CaO 18-35% of the ash
MgO 3-10% of the ash
Na20 0-3% of the ash
K20 0-1% of the ash
S03/other 6-20% of the ash

[0030] The invention provides a method for controlling slag properties in
a cyclone combustor, which comprises: determining the need, location,
dosage amount and targeting information of a boron composition necessary
for slag modification for proper viscosity; and providing precise dosing
as to location and amount of a boron composition in a suitable vehicle,
e.g., slurry, particulate solid or solution form, by controlled feeding
through injection ports on each cyclone barrel such that the boron
composition, e.g., borate, borax or blend, lowers the melt point of the
slag while making slag thicker (more plastic), causing a protective layer
of slag to form on the cyclone barrel inside wall, but still able to flow
to drains.

[0031] In one aspect, the invention achieves uniform contact of the
burning coal with a precise amount of a boron composition fluxing agent
to improve the flow properties of the slag to assure proper cyclone
furnace operation with coals having low iron and high calcium contents.

[0032] Preferably, as will be explained in greater detail below with
specific regard to FIGS. 3 to 5, direct observation or computational
fluid dynamics (CFD) or other computer or cold flow modeling will be
employed to determine the location of injection ports on each cyclone
barrel such that the boron composition modifies the melt point of the
slag while making slag suitably viscous (e.g., plastic), causing a
protective layer of slag to form on the cyclone barrel inside wall, but
still able to flow to drains. By virtue of the correct calculation and
the correct selection of boron compositions, the present invention can
provide precise dosing as to location and amount of a boron composition.
The disclosures of U.S. Pat. No. 5,740,745, U.S. Pat. No. 5,894,806 and
U.S. Pat. No. 7,162,960, all to the inventor herein with others, are
incorporated by reference herein for their descriptions of suitable
computational fluid dynamics and other modeling techniques.

[0033] The boron composition used according to the invention can be a
member selected from the group consisting of borax, borates, boric and
blends of two or more of these. In particular, borax or boric acid, and
sodium borate can be employed. They can be effective alone or with a
carbonate or sulfate boron salt, or the like, e.g., as a stabilized boric
acid blend, and will be employed in a suitable physical form, e.g.,
particulate solid or solution, in a suitable, preferably liquid, vehicle
such as water as a slurry, dispersed solid or solution, or in air,
controlled feeding through injection ports on each cyclone barrel such
that the boron composition, e.g., borate, borax or blend, lowers the melt
point of the slag while making slag thicker (more plastic), causing a
protective layer of slag to form on the cyclone barrel inside wall, but
still able to flow to drains. The composition can be a boron composition
and may also include alkali hydrates. In some cases, the boron
composition can be stopped and the alkali hydrates can be started or
continued. Exemplary of the alkali hydrates are soda ash, coal ash,
sodium salts with alkalinity, phosphorous compounds, and the like, which
like the boron composition will be employed in a suitable physical form.
The boron composition mixes with the swirling gas in the cyclone burner.
The swirling air flow in the burner 10 can be best seen from the flow
lines in FIG. 1. The boron composition is exposed to sodium in the flux
and is believed to convert to sodium borate that does the fluxing in the
cyclone barrel.

[0034] The technology of the invention allows precise targeting of the
cyclone barrel walls with the precise amount of boron composition
required to achieve the goal, 100% coverage and no more. While mixing at
the slag surface will be problematical when a fluxing agent is simply
added with the fuel or air fed to a combustor, the ability of the
invention to provide precise targeting enhances the mixing. An advantage
of this approach is that the invention is highly effective as a remedial
measure when slagging anomalies are identified. Doses may be increased
for a time period as necessary to achieve mixing and slag modification.

[0035] It will be seen that the doses of the boron compositions according
to the present invention can be reduced from what might otherwise be
necessary without precise dosing. Typically, the boron composition will
be introduced in amounts as low as about 0.1 pounds per ton of PRB or
like coal. Preferred dosings in many cases will be less than 1.0 pounds
per ton of PRB coal, e.g., from 0.2 to about 0.5 pounds per ton of PRB
coal.

[0036] In addition to treating the slag in the cyclone barrel at the
cyclone barrel walls, the boron composition material can be
advantageously applied in a targeted fashion to the water-walls of the
boiler furnace to react with slag thereon to either insulate heat
transfer and allow steam temperature to be maintained in the superheaters
of boilers where superheat temperature is too low due to high furnace
water-wall area, or in a blend with other metal oxides, to improve heat
transfer on the water-walls by decreasing reflectivity of high alkaline
earth oxide containing boiler ash.

[0037] To best understand the invention, we first refer to FIGS. 1 and 2,
which are schematic representations of a cyclone furnace combustor 10.
The first, FIG. 1 shows the prior art with material flows of air, coal
and slag, while FIG. 2 shows one embodiment of the invention wherein the
boron composition is added to the cyclone burner through separate
injectors 20, and FIG. 3 shows the introduction of the boron composition
with secondary air 15. This type of introduction is greatly benefited by
the use of computational fluid dynamics that will enable complete
coverage of exposed slag surfaces in the cyclone, as will be explained in
greater detail below.

[0038] The combustor includes a barrel 12, a re-entrant throat 14,
secondary air inlet 15, and slag tap opening 16 through which slag 17
flows out. In operation of the apparatus as shown, crushed coal is fed,
preferably with the primary air, through feed opening 18. Coal is
desirably fed in particulate form and particles are thrown outward as the
flow spins through the barrel as shown by the arrows (the flame 13,
generally shown in FIG. 3, will swirl like the arrows). This flow of air
and fuel is caused by the tangential flow imparted by the manner of
introducing the air and coal. This flow creates a region of high heat
release adjacent the refractory lining of the barrel wall. The high
temperature in this region causes the ash contained within the coal to
melt. The molten slag 17 acts as a trap for the carbon-rich coal
particles, retaining the particles for a period of time enabling a high
degree of carbon burnout. The molten slag 17 eventually migrates forward
along the wall of the barrel, exits at the slag spout opening 16, and
continuously drains through a slag tap opening 16 located below the
re-entrant throat 14. Tertiary air is shown to be fed to the burner at
the tertiary air inlet 19, and secondary air (the main combustion air)
enters the cyclone combustor at the secondary air inlet 15. Reference to
FIGS. 1 and 3 shows the slag emptying from the furnace 30 via a slag tap
32.

[0039] The flow of slag 17 from the cyclone burner at the proper rate with
PRB coal is assured by the invention, which introduces the boron
composition in a manner that it treats the upper surface of the flow of
slag 17. The boron composition is provided as a fine powder, preferably
from drying a solution or suspension by hot air in an air duct such as 52
in FIGS. 3 and 4. While not wishing to be bound to any particular theory
of operation, the treatment at the surface of the slag with the
finely-divided boron composition as opposed to the whole mass of it helps
explain how the invention can operate effectively with very low
consumption of born composition. In the arrangement shown in FIG. 2, a
borate or other boron composition is introduced via feed 20. In preferred
embodiments, such as illustrated in FIGS. 3 to 5, the borate or other
boron composition will be fed as part of the secondary air 15.

[0040] Reference to FIG. 3 will show the general orientation of the
combustor 10 in the furnace 30, which is partially cut away at the bottom
to show flame 13. In actual practice, the barrel 12 will be on the
outside of the furnace 30 and the reentrant throat 14 and the slag tap
opening 16 will be on the inside.

[0041] The control system illustrated in FIG. 5 is representative of those
that can be employed and preferably includes sensors indicated in the
drawings by a symbol which comprises the letter "X" in a box (very
small), and electrical connectors shown as dotted lines. The connectors
can be hard-wired or wireless. The control system includes a controller
40 as shown with a monitor or other reporting device, which will receive
signals from the various sensors, calculate the appropriate control
response by feed forward and feedback logic and send control signals to
the various pumps shown in the drawings as a triangle within a circle.
The controller 40 will control both the coal feed 18 and a borate or
other boron composition feed 21 as necessary to provide precise targeting
of the borate compound onto the surface of the slag within the barrel 12
in a manner that enhances the contact of the boron composition with the
slag layer 17. It is an advantage of the invention that the dosing can
also be highly effective as a remedial measure when slagging anomalies
are identified. As noted, doses may be increased for a time period as
necessary to achieve mixing and slag modification.

[0042] The boron composition will be fed from injectors 20 in FIG. 2 or 54
in FIG. 4, in a suitable vehicle, e.g., slurry, particulate solid or
solution form, by controlled feeding through injection ports on each
cyclone barrel 12 such that the boron composition, e.g., borate, borax or
blend, lowers the melt point of the slag while making slag thicker (more
plastic), causing a protective layer of slag to form on the cyclone
barrel 12 inside wall, but still able to flow to drains 16. The boron
composition is provided as a fine powder, preferably from drying a
solution or suspension by hot air in an air duct such as 52 in FIGS. 3
and 4. The gas flow makes a swirling pattern as it moves from the
entrance end of the burner 10 and the coal source 18 upstream within an
annular region, exiting from the barrel through the reentrant throat 14
into the furnace 30.

[0043] Preferably, the boron composition is introduced as determined by
computational fluid dynamics (CFD), which can be used to determine the
location of injection ports within ducts 52 as shown in FIGS. 3 and 4. To
get the best distribution, each cyclone barrel is individually modeled to
help determine the concentration of the boron composition solution or
suspension, the size of droplets sprayed from nozzles 54, the direction
and velocity of the spray, for given gas flow and temperature
measurements within duct 52. Nozzles 54 will be capable of forming fine
sprays, and their final selection will depend on the results of the CFD
modeling. The particles of the boron composition after spray and drying
will be very fine, on the order of 0.1μ on a weight average basis. In
preferred embodiments the boron compositions will be sprayed as soluble
compositions to form dry salts in finely divided form.

[0044] The use of modeling can assure that the boron composition is
properly administered in accord with the disclosures of U.S. Pat. No.
5,740,745, U.S. Pat. No. 5,894,806 and U.S. Pat. No. 7,162,960, which are
incorporated by reference herein for their descriptions of suitable
computational fluid dynamic and other modeling techniques. Once a model
for a given combustor is made, further similar units can take advantage
of that as following that iteration of the inventive process. FIG. 4
illustrates a single secondary air feed duct 52 having a transition 53 to
a secondary air duct 15, which is oriented to direct the air tangentially
into cyclone burner 10. The secondary air feed duct 52 contains within
its interior a nozzle 54 for spraying a solution or suspension of boron
composition. The hot, preheated air from preheater 34 in FIG. 3 moves
rapidly through the duct as the spray pattern 56 is seen to enlarge
radially without contacting the interior surfaces of the duct 52 while it
is wet. If contact were to occur, deposits of boron composition would
form and ultimately cause problems.

[0045] Process operating variations and physical combustor designs will
cause the temperature of the hot air in duct 52 to vary. However, it is
desired to use a temperature of above about 300° F., and
preferably within the range of from 400° to 700° F. If
needed, supplemental heaters can be employed. It is attempted in the
drawing by means of shading to show that at a point approximately at 58,
the spray will be dry and covering about 80 to 99%, e.g., 90%, of the
area of the duct 52. The modeling should determine that first contact of
the injected materials with the wall should occur no sooner than where
drying finally occurs and the boron composition is in a fine powder form,
the wall have not been significantly wetted with the solution or
suspension. The modeling preferably takes into account the whole length
of duct 52 from the point of introduction to at least the transition 53,
and preferably into secondary air duct 15 and most preferably to final
introduction into cyclone burner 10.

[0047] A computational fluid dynamics software package called "PHOENICS"
(Cham. LTD.), has been found effective. This program and others can solve
a set of conservation equations in order to predict fluid flow patterns,
temperature distributions, and chemical concentrations within cells
representing the geometry of the physical unit. It has been found helpful
to also run, in addition to the standard program features, a set of
subroutines to describe flue gas properties and injector characteristics
which for utilization in the solution of the equations.

[0048] Typical sprays produce droplets with a range of sizes traveling at
different velocities and directions. These drops interact with the flue
gas and evaporate at a rate dependent on their size and trajectory and
the temperatures along the trajectory. Improper spray patterns and
improper location are typical of prior art slag reducing procedures and
result in less than adequate chemical distributions and lessen the
opportunity for effective treatment.

[0049] A frequently used spray model is the PSI-Cell model for droplet
evaporation and motion, which is convenient for iterative CFD solutions
of steady state processes. The PSI-Cell method uses the gas properties
from the fluid dynamics calculations to predict droplet trajectories and
evaporation rates from mass, momentum, and energy balances. The momentum,
heat, and mass changes of the droplets are then included as source terms
for the next iteration of the fluid dynamics calculations, hence after
enough iterations both the fluid properties and the droplet trajectories
converge to a steady solution. Sprays are treated as a series of
individual droplets having different initial velocities and droplet sizes
emanating from a central point. Correlations between droplet trajectory
angle and the size or mass flow distribution are included, and the
droplet frequency is determined from the droplet size and mass flow rate
at each angle.

[0050] The correlations for droplet size, spray angle, mass flow droplet
size distributions, and droplet velocities are found from laboratory
measurements using laser light scattering and the Doppler techniques.
Characteristics for many types of nozzles under various operating
conditions have been determined and are used to prescribe parameters for
the CFD model calculations.

[0051] The above description is for the purpose of teaching the person of
ordinary skill in the art how to practice the invention. It is not
intended to detail all of those obvious modifications and variations,
which will become apparent to the skilled worker upon reading the
description. It is intended, however, that all such obvious modifications
and variations be included within the scope of the invention which is
defined by the following claims. The claims are meant to cover the
claimed components and steps in any sequence which is effective to meet
the objectives there intended, unless the context specifically indicates
the contrary.